This invention relates to a conductive tightening member molded from synthetic resin.
Conventionally, a tightening member molded from hard synthetic resin such as nylon is put in a tapped hole of a machine element to fix the machine element, because the synthetic resin tightening member is easily and cheaply manufactured and light in weight.
As is generally known, synthetic resin is an insulator and is prone to be electrified with static electricity. Therefore, the synthetic resin tightening member, when utilized in a copying machine or the like, sometimes suffers from electrification as a result of static electricity caused by friction so that the copying machine operates incorrectly. To solve this problem, a tightening member molded from synthetic resin containing conductive material such as carbon black and metallic particles has been created.
Although a tightening member molded from synthetic resin containing carbon black has low electric resistivity and can prevent electrification by static electricity, the amount of carbon black has an upper limit because the mixed carbon black deteriorates mechanical properties such as the strength of the synthetic resin.
Moreover, even when the amount of carbon black is below the upper limit, a slight increase of the amount of carbon black sharply reduces the volume resistivity of synthetic resin when the volume resistivity is between 10.sup.10 .OMEGA..multidot.cm and 10.sup.3 .OMEGA..multidot.cm, where the synthetic resin containing carbon black most effectively prevents electrification by static electricity. Therefore, it is quite difficult to mix carbon black in the synthetic resin such that volume resistivity is set at the optimum value between 10.sup.10 .OMEGA..multidot.cm and 10.sup.3 .OMEGA..multidot.cm.
On the other hand, the problem of a tightening member molded from synthetic resin containing metallic particles is that the metallic particles are prone to being unevenly dispersed in the synthetic resin because the metallic particles and the synthetic resin are not compatible with each other and their specific gravities are quite different. The molded tightening member thus has an uneven volume resistivity and, accordingly, cannot effectively prevent electrification by static electricity.